Definatly Blu-ray at ~10* read speed it's fast enough to read 25Gb in under 10 minutes and i expect eventually PS3's will appear with 4* and 6* speed blu-ray drives (just like the PS2 or Xboxes have done with DVD)
I doubt there will ever be a need to go to a larger optical format for games or movies blu-ray has enough head room to allow for 2k48 and 3D Hi Definition formats (especially once they develop 3D codecs ).
Wiki claims current Blu-ray drives should be able to read the 4 layer 100GByte disks made by hitachi if 50Gb is not enough (after a firmware update). I doubt that will happen though each optical layer increases the manufacturing costs of optical media. VMD was dead on arrival due to higher costs and lower capacity than both the blu-lazer formats.
PS3 number 1 fan
